Wireless power transfer (WPT) includes wireless techniques for charging of battery powered devices. This wireless charging operates using close proximity between the charging source and the device to be charged. For example, WPT technologies such as near-field manetoquasistatic (MQS) WPT and inductive charging are capable of charging a device (e.g., one or two devices) by bringing the device into close proximity with a charging source. This wireless charging technique commonly includes inducing a current in the device to be charged by placing it on or in close proximity with the power source. Common examples include charging an electric toothbrush in a charging stand, using a power transfer mat upon which a mobile device is laid, etc.
WPT also includes a power source providing a small amount of power for certain device devices at a distance. For example, broadcast far-field WPT is capable of transferring power at greater distances, e.g., to a radio frequency identification (RFID) tag. However, this broadcast technique is not efficient in that commonly less than 0.1% of the source power is provided to the target device. Moreover, regulations often (which vary by jurisdiction) limit the amount of power transferred using such techniques to approximately 100 uW. While point-to-point far-field WPT systems maintain higher end-to-end efficiency, these techniques require complex control and tracking mechanisms to maintain a line of sight connection between the power source and the target and are likewise limited in the amount of power that they can deliver.